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Last time, I talked about how sometimes, in big seas, you can see foam floating on the surface, and snarled on the beach. This foam is made from millions of bubbles, and sometimes it can be metres thick.

I also described how this foam happens when bubbles (which are usually quite unstable) are made stable by slowing down the rate at which the liquid drains out of the thin wall of the bubble. You can do this by reducing the surface tension, or making the liquid more viscous, or by adding particles to it.

Reducing surface tension is what detergents do, and so natural detergents will help make a foam much more stable. Hydrophilic (that is, "fat-hating") particles can slow down enormously the rate at which water drains out of the bubble wall.

On average, sea foam happens because of natural detergent-like chemicals that sit in the surface microlayer. These chemicals typically come from phytoplankton blooms, seaweed or even terrestrial plants. The waves, especially in big seas, can whisk these chemicals into a foamy mass.

Of course, foams in different parts of the world will have different chemical make-ups. So foam near kelp beds might show that proteins make up 20 per cent of the dried weight, followed by fats at 6 per cent and carbohydrates at 2 per cent.

Looking at sea foam another way (in terms of living creatures), one worker found that sea foam was made up of about 25 per cent solid matter — mostly bacteria and diatoms, but there were also significant numbers of dinoflagellates and both green algae and blue-green algae. In this study, the majority of creatures found in the sea foam were not floating freely like plankton, but instead, were mostly attached to either sediments or plants.

But these proportions will depend enormously on what's around in the local environment.

Now sea foams are not inherently bad or good for the environment — again, it all depends on local effects.

So on one hand, aquatic foams can be both a food supply and a place to live for various organisms. They can concentrate carbon and other nutrients, and can be a site for nutrient recycling. Fish and waterfowl often feed on foam. Foam in freshwater can also increase fertilisation success, and retention of eggs and larvae in fish that build nests, and in tropical aquatic frogs.

But on the other hand, the foam can be so thick that young children can miss their footing while walking through it, and even drown.

The foam can also sometimes concentrate metals (such as zinc, copper and lead), hydrocarbons, pesticides and natural toxins. It can then carry these toxins into living creatures via the food chain.

In one case, an especially protein-rich foam that came from a red tide bloom washed over marine birds. The foam was not toxic, but it was similar to soap in that it removed the normal water repellence from the birds' feathers. As a result, the foam made it harder for the birds to fly, and many died of hypothermia.

In another case, a bloom of dinoflagellates in the Eastern Pacific produced a mucus-rich foam that actually suffocated some corals.

Foam can potentially infect humans. Bubbles in the ocean can pick up and carry viruses. When these bubbles that make up foam break and pop open, they squirt the viruses into the air on tiny jets of seawater.

These jets are now aerosols and can be spread by the wind, putting humans at risk of exposure to viruses and other pathogens — and in some cases, toxins.

One study deliberately injected viruses into the surf, and found that the concentration of viruses in the aerosol droplets was 200 times higher than in the water in the surf. As you would expect, the virus level decreased the further you went downwind from the surf.

But in its natural form, sea foam at the shore ain't that bad. As they say: "Worse things happen at sea"...